1. Field of the Invention
This invention relates to a method of and an apparatus for detecting the maximum cylinder pressure angle in an internal combustion engine, and more particularly to a method of and an apparatus for detecting the maximum cylinder pressure angle in an internal combustion engine which enables accurate detection of the maximum pressure angle by using the actual piston top dead center (TDC) position as the basis for correcting for error arising in detection of a reference crankshaft angular position required for determining the maximum cylinder pressure angle.
2. Description of the Prior Art
There are known methods or apparatuses for detecting the cylinder pressure of an internal combustion engine and then controlling engine operation, such as the ignition timing thereof on the basis of the angle at which the cylinder pressure becomes maximum. For example, Japanese Laid-open Patent Publication No. 56(1981)-101071 discloses an apparatus in which a reference crankshaft angle such as top dead center (TDC) is detected by use of a crankshaft angle sensor and the position at which the maximum cylinder pressure occurs (the maximum pressure angle .theta. pmax) is determined based on the reference crankshaft angle.
As the crankshaft angle sensor there is generally used an electromagnetic pickup or any other detecting element such as an electromagnetic resistive element, a Hall element or a photo-element. Particularly when an electromagnetic pickup is used, however, there arises a detection lag caused by inductance so that it is impossible to accurately detect the reference crankshaft angle. As a result, an error arises in the detection of the maximum pressure angle and engine operation such as an ignition timing cannot be controlled accurately. Moreover, irrespective of what kind of sensor is employed, detection error will arise if there is any error in the position at which the sensor is attached to the crankshaft or the like. It has also been difficult to avoid errors in sensor output resulting from inevitable variance among individual sensors.
One method that has been used for overcoming these problems has been to experimentally determine data required for compensation in advance and to store this data in a memory constituting a part of the control device for controlling the operation of the internal combustion engine. In this case too, however, it is necessary to accurately mount the crankshaft angle sensor at the prescribed position and, at any rate, it is still impossible to compensate for variance among individual sensors.
FIG. 1 shows data experimentally obtained by the inventor regarding the detection lag (deviation angle) of a crankshaft angle sensor. As will be noted from this graph, the angle of detection deviation increases with increasing engine speed and the amount of deviation increases substantially linearly with increasing speed. Apart from the above, it should also be noted that it is a well-known fact that during motoring (when there is no explosive combustion of air-fuel mixture, i.e. during non-firing) the cylinder pressure becomes maximum at piston TDC.